T cell lymphomas have been demonstrated to express differentiated surface Ly antigen phenotypes similar to those of normal peripheral T cell sub-populations. These phenotypes are stable in vivo with tumor transplantation and in vitro with established culture lines. A neonatal thymic suppressor cell subpopulations enriched by treatment with mouse thymic virus was demonstrated to express a different Ly phenotype (Ly 1, 2, 3 plus) from antigen-specific suppressor cells in adults (Ly 2, 3 plus). BIBLIOGRAPHIC REFERENCES: Greenberg, R.S., Mathieson, B.J., Campbell, P.S. and Zatz, M.: Multiple occurrence of spontaneous AKR/J lymphomas with T and B cell characteristics. J. Immunol. 118: 1181-1190, 1977. Mosier, D.E., Mathieson, B.J. and Campbell, P.S.: Ly phenotype and mechanism of action of mouse neonatal suppressor T cells. J. Exp. Med. 146: 59-73, 1977.